﻿/*
 * THIS PEACE OF CODE WAS TAKEN FROM 
 * Json.Net (http://json.codeplex.com)
 * PUBLISHED UNDER THE FOLLOWING LICENSE:
 *  
 * The MIT License (MIT)
 * 
 * Copyright (c) 2007 James Newton-King
 * 
 * Permission is hereby granted, free of charge, to any person obtaining 
 * a copy of this software and associated documentation files (the "Software"), 
 * to deal in the Software without restriction, including without limitation 
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the 
 * Software is furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included 
 * in all copies or substantial portions of the Software.
 * 
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
 *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 
 *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
 *  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 *  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 
 *  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE 
 *  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *  
 */
using System;
using System.Collections.Generic;

namespace GeoAPI.Utilities
{
    public class ThreadSafeStore<TKey, TValue>
    {
        private readonly object _lock = new object();
        private Dictionary<TKey, TValue> _store;
        private readonly Func<TKey, TValue> _creator;

        public ThreadSafeStore(Func<TKey, TValue> creator)
        {
            if (creator == null)
                throw new ArgumentNullException("creator");

            _creator = creator;
        }

        public TValue Get(TKey key)
        {
            if (_store == null)
                return AddValue(key);

            TValue value;
            if (!_store.TryGetValue(key, out value))
                return AddValue(key);

            return value;
        }

        private TValue AddValue(TKey key)
        {
            TValue value = _creator(key);

            lock (_lock)
            {
                if (_store == null)
                {
                    _store = new Dictionary<TKey, TValue>();
                    _store[key] = value;
                }
                else
                {
                    // double check locking
                    TValue checkValue;
                    if (_store.TryGetValue(key, out checkValue))
                        return checkValue;

                    Dictionary<TKey, TValue> newStore = new Dictionary<TKey, TValue>(_store);
                    newStore[key] = value;

                    _store = newStore;
                }

                return value;
            }
        }
    }
}